Variable stiffness and damping MR isolator

Abstract

This paper presents the development of a magnetorheological (MR) fluid-based variable stiffness and damping isolator for vibration suppressions. The MR fluid isolator used a sole MR control unit to achieve the variable stiffness and damping in stepless and relative large scope. A mathematical model of the isolator was derived, and a prototype of the MR fluid isolator was fabricated and its dynamic behavior was measured in vibration under various applied magnetic fields. The parameters of the model under various magnetic fields were identified and the dynamic performances of isolator were evaluated. 1. Introduction Vibration isolation systems are used to separate the vibration excitation source and the object to be protected in order to reduce the negative effect from the unwanted vibration from the vibration excitation source. Conventional vibration systems are in passive mode, for the intrinsic limitation of passive suspension system, the improvement is effective only in a certain frequency range, because passive design for low frequency is difficult and often represents a compromise between isolation performance and the supported machinery alignment [1]. It is possible to improve the isolation performance over a wide range of frequency by active vibration control. However, active vibration isolation systems are less commonly used than passive systems due to their associated cost, power requirements, complexity and fail-safe problems [2, 3]. Semi-active suspensions can be nearly as effective as fully active suspensions in vibration suppression. They do not require either higher-power actuators or a large power supply. When the control system fails, the semi-active suspension can still work in a passive condition. In early semi-active suspension systems, the adjustable damping force can be achieved by using hydraulic semi-active dampers with electromagnetically controlled valves or Friction damper, of which the damping force is controlled by varying the force normal to a friction interface. More recently, with the introduction of Magnetorheological (MR) fluid, it is easy to achieve the variable damping with an MR damper in isolation system. The effort to improve the performance of the isolation systems by using a variable damping damper based on MR fluid has been done by many researchers [4-5]. However, variable damping and stiffness systems showed significant improvements in vibration reduction application, such as the seismic protection system [6] and the vehicle suspension [7]. However, all the methods to achieve variable stiffness in these devices are usually complicated and low reliability, and it is difficult to accomplish stepless control on the stiffness [8]. Kobori et al. developed a variable stiffness system for protecting the building from the earthquakes [9]. A valve in a cylinder device was controlled in open/close ways to lock and unlock the connection between the beam and the brace and two alternative stiffnesses were produced at each floor. Youn et al. developed a vehicle suspension using